In trucks, it is common to provide a pair of parallel spaced-apart frame rails of C-shaped cross section which extend the length of the truck. In one prior art approach, the frame rails are of steel of a C-shaped cross section with a vertical web portion and upper and lower flange portions of a constant thickness, with the thickness of the flanges being equal to the thickness of the webs. Aluminum frames have also been manufactured with frame rails of a C-shaped cross section with a web portion of a constant thickness and web flanges which are of a constant thickness but of a thickness which differs (e.g. is thicker than) from the thickness of the web portion.